Cory C. Bomberger

Enhanced room temperature electronic and thermoelectric properties of the dilute bismuthide InGaBiAs

We report room temperature electronic and thermoelectric properties of Si-doped In0.52Ga0.48BiyAs1−y with varying Bi concentrations. These films were grown epitaxially on a semi-insulating InP substrate by molecular beam epitaxy. We show that low Bi concentrations are optimal in improving the conductivity, Seebeck coefficient, and thermoelectric power factor, possibly due to the surfactant effects of bismuth. We observed a reduction in thermal conductivity with increasing Bi concentration, which is expected because of alloy scattering. We report a peak ZT of 0.23 at 300 K.

Comparison of thermal annealing effects on electrical activation of MBE grown and ion implant Si-doped In0.53Ga0.47As

The effect of thermal annealing on the net donor concentration and diffusion of Si in In0.53Ga0.47As is compared for electrically active layers formed by ion implantation versus molecular beam epitaxy (MBE). Upon thermal treatment at temperatures of 700 °C or higher for 10 min, both ion implanted and growth-doped substrates converge to a common net donor solubility. These results indicate that while MBE doped substrates typically exhibit higher active concentrations relative to implanted substrates, the higher active Si concentrations from MBE growth are metastable and susceptible to deactivation upon subsequent thermal treatments after growth. Active Si doping concentrations in MBE doped material and ion-implanted materials are shown to converge toward a fixed net donor solubility limit of 1.4 × 1019 cm−3. Secondary ion mass spectroscopy of annealed samples indicates that the diffusivity of Si in MBE doped substrates is higher than those of ion implanted substrates presumably due to concentration-depende...

Single-material semiconductor hyperbolic metamaterials.

Layered semiconductor hyperbolic metamaterials for the mid-infrared are grown by molecular beam epitaxy using a single material system, doped and undoped InAs. The onset wavelength for metamaterial behavior can be tuned from 5.8μm to beyond 10μm, while the fill factor ranges from 0.25 to 0.75, resulting in designer optical behavior. The reflection and transmission behavior were studied by Fourier transform spectroscopy and modeled using effective medium theory. We also conducted a geometric optics experiment to demonstrate negative refraction of our materials.

Cross-plane thermoelectric transport in p-type La0.67Sr0.33MnO3/LaMnO3 oxide metal/semiconductor superlattices

The cross-plane thermoelectric transport properties of La0.67Sr0.33MnO3 (LSMO)/LaMnO3 (LMO) oxide metal/semiconductor superlattices were investigated. The LSMO and LMO thin-film depositions were performed using pulsed laser deposition to achieve low resistivity constituent materials for LSMO/LMO superlattice heterostructures on (100)-strontium titanate substrates. X-ray diffraction and high-resolution reciprocal space mapping indicate that the superlattices are epitaxial and pseudomorphic. Cross-plane devices were fabricated by etching cylindrical pillar structures in superlattices using inductively, this coupled-plasma reactive-ion etching. The cross-plane electrical conductivity data for LSMO/LMO superlattices reveal a lowering of the effective barrier height to 223 meV as well as an increase in cross-plane conductivity by an order of magnitude compared to high resistivity superlattices. These results suggest that controlling the oxygen deficiency in the constituent materials enables modification of the...

Implantation and Diffusion of Silicon Marker Layers in In0.53Ga0.47As

Continued effort has been placed on maximizing activation while controlling the diffusion of silicon doping in InGaAs for present and future complementary metal-oxide semiconductor devices. In order to explore the diffusion and activation behavior, Si marker layers were grown in InGaAs on InP by molecular beam epitaxy. The nature of Si diffusion was explored using a series of isoelectronic implants to introduce excess point defects near the layer. It was observed that excess interstitials reduce the Si diffusion consistent with a vacancy-driven diffusion mechanism. A diffusion and activation model implemented in the Florida object oriented process simulator has been developed to predict silicon diffusion behavior over a variety of temperatures and times. Using current and previous experimental data and complimentary density functional theory results, the diffusion model employs the SiIII–VIII pair as the primary mechanism for silicon diffusion in InGaAs.

Determining the band alignment of TbAs:GaAs and TbAs:In0.53Ga0.47As

We propose and systematically justify a band structure for TbAs nanoparticles in GaAs and In0.53Ga0.47As host matrices. Fluence-dependent optical-pump terahertz-probe measurements suggest the TbAs nanoparticles have a band gap and provide information on the carrier dynamics, which are determined by the band alignment. Spectrophotometry measurements provide the energy of optical transitions in the nanocomposite systems and reveal a large blue shift in the absorption energy when the host matrix is changed from In0.53Ga0.47As to GaAs. Finally, Hall data provides the approximate Fermi level in each system. From this data, we deduce that the TbAs:GaAs system forms a type I (straddling) heterojunction and the TbAs:In0.53Ga0.47As system forms a type II (staggered) heterojunction.

Growth and characterization of ErAs:GaBix As1−x

We explore the growth and characterization of ErAs:GaBiAs as a candidate material for terahertz generation and detection via photoconductive switches. Spectrophotometry shows that the incorporation of small amounts of bismuth causes a reduction in the band gap, making these materials compatible with fiber-coupled lasers. ErAs pins the Fermi level within the band gap, causing high dark resistance while maintaining high mobility, shown by Hall effect measurements. Finally, transient absorption (optical pump, optical probe) measurements show that the ErAs provides a carrier recombination pathway, causing short carrier lifetimes. These material properties make ErAs:GaBiAs an interesting choice for fiber-coupled photoconductive switches.

Observation of Self-Assembled Core–Shell Structures in Epitaxially Embedded TbErAs Nanoparticles

Self-assembled core-shell structured rare-earth nanoparticles (TbErAs) are observed in a III-V semiconductor host matrix (In0.53Ga0.47As) nominally lattice-matched to InP, grown via molecular beam epitaxy. Atom probe tomography demonstrates that the TbErAs nanoparticles have a core-shell structure, as seen both in the tomographic atom-by-atom reconstruction and concentration profiles. A simple thermodynamic model is created to determine when it is energetically favorable to have core-shell structures; the results strongly agree with the observations.

Review Article: Overview of lanthanide pnictide films and nanoparticles epitaxially incorporated into III-V semiconductors

The incorporation of lanthanide pnictide nanoparticles and films into III-V matrices allows for semiconductor composites with a wide range of potential optical, electrical, and thermal properties, making them useful for applications in thermoelectrics, tunnel junctions, phototconductive switches, and as contact layers. The similarities in crystal structures and lattice constants allow them to be epitaxially incorporated into III-V semiconductors with low defect densities and high overall film quality. A variety of growth techniques for these composites with be discussed, along with their growth mechanisms and current applications, with a focus on more recent developments. Results obtained from molecular beam epitaxy film growth will be highlighted, although other growth techniques will be mentioned. Optical and electronic characterization along with the microscopy analysis of these composites is presented to demonstrate influence of nanoinclusion composition and morphology on the resulting properties of the composite material.The incorporation of lanthanide pnictide nanoparticles and films into III-V matrices allows for semiconductor composites with a wide range of potential optical, electrical, and thermal properties, making them useful for applications in thermoelectrics, tunnel junctions, phototconductive switches, and as contact layers. The similarities in crystal structures and lattice constants allow them to be epitaxially incorporated into III-V semiconductors with low defect densities and high overall film quality. A variety of growth techniques for these composites with be discussed, along with their growth mechanisms and current applications, with a focus on more recent developments. Results obtained from molecular beam epitaxy film growth will be highlighted, although other growth techniques will be mentioned. Optical and electronic characterization along with the microscopy analysis of these c...